Examining Metastatic Potential in Mammary Stem Cells

Institution: University of California, San Diego
Investigator(s): Jay Desgrosellier, Ph.D. -
Award Cycle: 2012 (Cycle 18) Grant #: 18IB-0020 Award: $150,000
Award Type: IDEA
Research Priorities
Biology of the Breast Cell>Biology of the Normal Breast: the starting point

Initial Award Abstract (2012)

In breast cancer, metastasis research has largely overlooked the contribution of the cell-of-origin. In humans, pregnancy-associated breast cancers represent some of the most lethal mammary tumors due to frequent metastasis. Mammary stem cells (MaSCs) increase dramatically during pregnancy suggesting a link between MaSCs and pregnancy-associated tumors. In addition, these MaSCs represent unique targets of oncogenic transformation in the adult mammary gland, distinct from more differentiated epithelial cells, and may be directly related to cancer stem cells (CSCs), a highly aggressive sub-population of cells present in some breast tumors.

In this project experiments will determine the relationship between mammary stem cells induced during pregnancy and cancer stem cells present in some of the most lethal breast tumors, including pregnancy-associated cancers. First, we will examine whether mammary stem cells from pregnant mice are more likely to form aggressive breast cancers and metastasize. This will be tested by adding a mutant protein to mammary stem cells that allows them to grow tumors in the mammary glands of mice. We will then determine whether these tumors grow larger or metastasize more frequently than other similar cell types in the mammary gland. Additionally, we will analyze these tumors for expression of biomarker proteins commonly associated with different breast cancer sub-types in people to determine any relationship between mammary stem cells and a particular type of breast cancer. Next, we will explore whether pregnancy regulates breast cancer stem cells and determine the molecular underpinnings of this association. This will be done by examining the behavior of breast cancer stem cells from mice genetically engineered to grow breast tumors. We will determine how these cancer stem cells behave in mice with at least one completed pregnancy compared to mice that have never been pregnant. Finally, we will test whether a molecule, called integrin alpha-v/beta-3, is required by cancer stem cells to grow tumors and metastasize.

These studies have the potential to re-shape our current understanding of epithelial cancer biology by determining the potential of MaSCs to contribute to breast CSCs and metastatic tumor cells. Additionally, these experiments may implicate MaSCs and the integrin alpha-v/beta-3 as critical players in pregnancy-associated breast cancer. From a therapeutic perspective, our findings may suggest that targeting integrin alpha-v/beta-3 ligand-binding or signaling will benefit breast cancer patients with pregnancy-associated tumors. In the long-term, results from these studies will open the door to future examination of signaling pathways critical to MaSC function in order to identify new therapeutic targets for combating aggressive breast cancers.

Final Report (2014)

Investigation into the association between pregnancy and breast cancer made the unexpected discovery that a recent pregnancy caused a transient increased risk of developing aggressive breast cancer. Characteristics of adult mammary stem cells are associated with aggressive breast cancers, suggesting that mammary stem cells present during pregnancy may contribute to these pregnancy-associated breast cancers. Therefore, the overall goal of these studies is to determine the relationship between mammary stem cells induced during pregnancy and cancer stem cells present in some of the most aggressive breast tumors including pregnancy-associated breast cancers.

To accomplish this goal I proposed to examine (1) whether mammary stem cells from pregnant mice are more likely to form aggressive breast cancers and (2) whether pregnancy regulates breast cancer stem cells via the protein integrin alpha v beta 3. As of the completion of this grant, great strides have been made and barriers overcome. Toward the first aim, we have now generated and characterized transformed cell lines and are preparing to test these cells using both in vitro and in vivo assays of tumorigenicity. In regards to aim 2, we have now completed collecting tumors from MMTV-Wnt1 mice with a genetic deletion of the integrin beta 3 subunit (?3KO) and characterized a delay in tumor formation. Preliminary experiments characterizing the cancer stem cell content of these tumors found fewer tumor initiating cells relative to tumors from WT mice. These findings, along with additional new insight discovered during the course of this project, will provide the basis for future studies into the role of pregnancy-associated mammary stem cells and their signaling pathways in breast cancer.

In summary, results from our studies have identified a critical role for the integrin ?v?3 in adult MaSCs during pregnancy. Unexpectedly, ?3 deletion in mice decreased activation of Slug, a master regulator of MaSCs, resulting in defective MaSC expansion and mammary morphogenesis during pregnancy. In human breast cancer cells, ?v?3 was necessary and sufficient for Slug activation that was associated with ?v?3-mediated anchorage-independent colony formation and tumor initiation, both hallmarks of cancer stem cells and highly aggressive tumor cells. As evidence of the impact of this work, a manuscript describing these findings was recently reviewed in the journal Developmental Cell and we are currently performing the necessary revisions to address the reviewers’ comments. These findings provide further evidence of a link between molecules driving mammary stemness during pregnancy and stem-like properties associated with some aggressive human breast cancers.

Integrin avb3 Drives Slug Activation and Stemness in the Pregnant and Neoplastic Mammary Gland.
Periodical:Developmental Cell
Index Medicus: Dev Cell
Authors: Desgrosellier JS, Lesperance J, Seguin L, Gozo M, Shumei K, ... Cheresh DA
Yr: 2014 Vol: 30 Nbr: 3 Abs: Pg:295-308